Flexible display apparatus

ABSTRACT

A display apparatus includes a flexible substrate and a first insulation layer disposed on the flexible substrate. The flexible substrate includes a bending area. The first insulation layer includes a first unevenness disposed over the bending area. The first unevenness includes two or more steps in at least a portion of the first unevenness.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.16/290,558, filed on Mar. 1, 2019, which is a Division of U.S. patentapplication Ser. No. 15/423,128, filed on Feb. 2, 2017, which claimspriority under 35 U.S.C. § 119 to Korean Patent Application No.10-2016-0012917, filed on Feb. 2, 2016 in the Korean IntellectualProperty Office, the disclosures of which are incorporated by referenceherein in their entirety.

TECHNICAL FIELD

One or more exemplary embodiments of the present invention relate to adisplay apparatus, and more particularly to a flexible displayapparatus.

DISCUSSION OF RELATED ART

Organic light-emitting display apparatuses may have relatively wideviewing angles, relatively high contrast ratios, and relatively shortresponse times.

Organic light-emitting display apparatuses may include thin filmtransistors and organic light-emitting devices are formed on asubstrate. The organic light-emitting devices may emit light duringoperation of the organic light-emitting display apparatus. The organiclight-emitting display apparatus may be used as a display unit of asmall product, such as a cellular phone. Alternatively, the organiclight-emitting display apparatus may be used as a display unit of alarge product, such as a television.

Organic light-emitting display apparatuses may be a flexible displayapparatus. The flexible display apparatus may include a flexiblesubstrate. The flexible substrate may include a glass substrate or asynthetic resin. Since the flexible substrate can be relatively easilybent, it may be difficult to handle the flexible substrate in amanufacturing process. Accordingly, cracks may occur in the being areaof the flexible display apparatus in the flexible substrate, which mayreduce a reliability of the flexible display apparatus.

SUMMARY

According to one or more exemplary embodiments of the present invention,a display apparatus includes a flexible substrate and a first insulationlayer. The flexible substrate includes a bending area. The firstinsulation layer is disposed on the flexible substrate. The firstinsulation layer includes a first unevenness disposed over the bendingarea. The first unevenness includes two or more steps in at least aportion of the first unevenness.

The first unevenness may be a depression comprising at least two stepsat different distances from the flexible substrate.

The first unevenness may have a stepped shape. The stepped shape may besunk toward a center of the first unevenness.

The first unevenness may have a V shape.

The first insulation layer may be an inorganic insulation layer.

A width of the first insulation layer may be less than about 1 mm.

The display apparatus may further include a plurality of pixels. Theplurality of pixels may be arranged over the bending area of theflexible substrate. The first unevenness may be disposed betweenadjacent pixels.

The flexible substrate may have a bending axis extending in onedirection. The first unevenness may extend in a direction substantiallyparallel to the bending axis.

The display apparatus may further include a second insulation layer. Thesecond insulation layer may be arranged over the first insulation layer.The second insulation layer may include a second unevenness. The secondunevenness may include two or more steps in at least a portion of thesecond unevenness.

The second unevenness may be arranged over the first unevenness.

The second insulation layer may be an inorganic insulation layer.

A thickness of a portion of the first unevenness of the first insulationlayer may be smaller than a thickness of a portion of the firstinsulation layer excluding the first unevenness.

The flexible substrate may include a first surface and a second surfaceopposite to the first surface. The flexible substrate may be bent suchthat the second surface at least partially faces itself. The firstinsulation layer may be arranged over the first surface of the flexiblesubstrate.

According to one or more exemplary embodiments of the present invention,a display apparatus includes a substrate, a semiconductor layer, a firstinsulation layer, a gate electrode, a second insulation layer, a sourceelectrode, and a drain electrode. The semiconductor layer is disposed onthe substrate. The first insulation layer is disposed on thesemiconductor layer. The gate electrode is disposed on the firstinsulation layer. The second insulation layer is disposed on the gateelectrode. The source electrode and the drain electrode are disposed onthe second insulation layer. The first insulation layer includes a firstunevenness. The first unevenness is located in at least one region ofthe first insulating layer. The second insulating layer includes asecond unevenness. The second unevenness is located in a regioncorresponding to the first unevenness.

The display apparatus may further include a third insulation layer and apixel electrode. The third insulation layer may be disposed on thesecond insulation layer. The pixel electrode may be disposed on thethird insulation layer.

The third insulation layer may include a third unevenness. The thirdunevenness may be located in a region corresponding to the firstunevenness.

The display apparatus may further include a fourth insulation layer, andintermediate layer, and an opposite electrode. The fourth insulationlayer may include an opening. The opening may expose at least a portionof the pixel electrode. The intermediate layer may be disposed on thepixel electrode. The opposite electrode may cover the intermediatelayer. The opposite electrode may face the pixel electrode.

The fourth insulation layer may include a fourth unevenness. The fourthunevenness may be located in a region corresponding to the firstunevenness.

The substrate may have a bending axis. The bending axis may extend inone direction. The first unevenness may extend in a directionsubstantially parallel to the bending axis.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the exemplary embodiments,taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic lateral view illustrating a flexible displayapparatus according to an exemplary embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view illustrating a bending areaof a flexible display apparatus of FIG. 1 according to an exemplaryembodiment of the present invention;

FIG. 3 is an enlarged cross-sectional view illustrating a portion III ofFIG. 2 according to an exemplary embodiment of the present invention;

FIG. 4 is a schematic cross-sectional view illustrating a bending areaof a flexible display apparatus according to an exemplary embodiment ofthe present invention; and

FIG. 5 is an enlarged cross-sectional view illustrating a portion V ofFIG. 4 according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As the present invention allows for various changes and numerousembodiments, exemplary embodiments of the present invention will beillustrated in the drawings and described in detail herein. Hereinafter,aspects and features of one or more exemplary embodiments of the presentinvention and methods of accomplishing the same will be described morefully with reference to the accompanying drawings; however the presentinvention may be embodied in many different forms and should not beconstrued as being limited to the embodiments set forth herein. Thosecomponents that are the same or are similar to components in otherfigures may be referred to by the same reference numeral in all of thefigures and redundant explanations may be omitted.

It will be further understood that when a layer, region, or component isreferred to as being “formed on” or “disposed on” another layer, region,or component, it can be directly or indirectly formed or disposed on theother layer, region, or component. Therefore, intervening layers,regions, or components may be present.

Sizes of components in the drawings may be exaggerated for convenienceof explanation and the following exemplary embodiments of the presentinvention are not limited thereto.

The x-axis, the y-axis and the z-axis are not limited to three axes ofthe rectangular coordinate system. For example, the x-axis, the y-axis,and the z-axis may be substantially perpendicular to one another or mayrepresent different directions that are not substantially perpendicularto one another.

FIG. 1 is a schematic lateral view illustrating a flexible displayapparatus according to an exemplary embodiment of the present invention.FIG. 2 is a schematic cross-sectional view illustrating a bending areaBA of a flexible display apparatus of FIG. 1 according to an exemplaryembodiment of the present invention. FIG. 3 is an enlargedcross-sectional view illustrating a portion III of FIG. 2 according toan exemplary embodiment of the present invention.

Referring to FIGS. 1 and 2, a flexible display apparatus 1 may include aflexible substrate 100. The flexible display apparatus 1 may alsoinclude a display unit 200. The display unit 200 may be arranged overthe flexible substrate 100. The display unit 200 may have a firstunevenness 230 a and a second unevenness 250 a. The first unevenness 230a and the second unevenness 250 a may be a depression. The depressionmay include at least two steps at different distances from the flexiblesubstrate 100.

The flexible substrate 100 may be flexible. The flexible substrate 100may include a metal material or a plastic material. The metal materialand the plastic material may have a relatively high heat resistance anda relatively high durability. The plastic material may include variousmaterials. For example, the plastic material may include polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI),polyethersulfone (PES), polyacrylate (PA), polyetherimide (PEI),polyphenylene sulfide (PPS), polyarylate (PAR), polycarbonate (PC),cellulose triacetate, cellulose acetate propionate (CAP), orpoly(arylene ether sulfone); however, exemplary embodiments of thepresent invention are not limited thereto.

The flexible substrate 100 may include a bending area BA. Referring toFIG. 1, the flexible substrate 100 may include non-bending areas NBA.The non-bending areas NBA may be disposed at sides of the bending areaBA. The non-bending areas NBA may be folded to face each other withrespect to the bending area BA; however, exemplary embodiments of thepresent invention are not limited thereto. The flexible substrate 100may only include the bending area BA. When the flexible substrate 100includes the bending area BA and the non-bending areas NBA, the bendingarea BA may be disposed at an edge portion of the flexible substrate100. Widths of the non-bending areas NBA disposed at sides of thebending area BA may be different from each other.

Meanwhile, the flexible display apparatus according to the presentembodiment may have a bendable characteristic. That is, the flexibledisplay apparatus may be formed to have a bendable characteristic sothat the display device can bend as needed, instead of being alwaysbended. In this case, when the display device is bent, the bent portionmay be defined as a bending area BA, and the other regions may bedefined as a non-bending area NBA.

The flexible substrate 100 may include a first surface 100 a. Theflexible substrate 100 may also include a second surface 100 b. Thesecond surface 100 b may be opposite to the first surface 100 a. Asillustrated in FIG. 1, at least a portion of the second surface 100 b ofthe flexible substrate 100 may be bent in order to face itself. Thefirst surface 100 a of the flexible substrate 100 may face the outsidein a bending state. The display unit 200 may be arranged over the firstsurface 100 a of the flexible substrate 100.

The display unit 200 may be arranged over the flexible substrate 100.The display unit 200 may include a plurality of pixels. For example, thedisplay unit 200 may be an organic light-emitting display unit or aliquid crystal display unit. The organic light-emitting display unit andthe liquid crystal display unit may include a plurality of thin filmtransistors TFT and a plurality of pixel electrodes 292. The pixelelectrodes 292 may be electrically connected to the thin filmtransistors TFT. The display unit 200 may also include a capacitor Cap.

FIG. 2 is a schematic cross-sectional view illustrating the bending areaBA of the flexible display apparatus 1 of FIG. 1 according to anexemplary embodiment of the present invention.

As illustrated in FIG. 2, the display unit 200 positioned in the bendingarea BA may include the first unevenness 230 a and the second unevenness250 a.

The display unit 200 may include a buffer layer 210. The buffer layer210 may be arranged over the flexible substrate 100. The buffer layer210 may include silicon oxide or silicon nitride. The buffer layer 210may planarize a surface of the flexible substrate 100. The buffer layer210 may also reduce or prevent impurities from infiltrating into asemiconductor layer 220 of the thin film transistor TFT. Thesemiconductor layer 220 may be disposed on the buffer layer 210.

A gate electrode 240 may be arranged above the semiconductor layer 220.A source electrode 260 s and a drain electrode 260 d may be electricallyconnected to each other when a voltage is applied to the gate electrode240. The gate electrode 240 may include a single layer. Alternatively,the gate electrode 240 may include multiple layers. The gate electrode240 may include one or more materials including aluminum (Al), platinum(Pt), palladium (Pd), silver (Ag), magnesium (Mg), gold (Au), nickel(Ni), neodymium (Nd), iridium (Ir), chrome (Cr), lithium (Li), calcium(Ca), molybdenum (Mo), titanium (Ti), tungsten (W), or copper (Cu);however, exemplary embodiments of the present invention are not limitedthereto. The one or more materials may be selected according toadhesiveness to an adjacent layer, surface smoothness of a stackedlayer, or processability.

A first insulation layer 230 may be disposed between the semiconductorlayer 220 and the gate electrode 240. The first insulation layer 240 mayprovide insulation between the semiconductor layer 220 and the gateelectrode 240. The first insulation layer 230 may be an inorganicinsulation layer. The first insulation layer 230 may include siliconoxide and/or silicon nitride.

A second insulation layer 250 may be arranged above the gate electrode240. The second insulation layer 250 may be an inorganic insulationlayer. The second insulation layer 250 may include a single layer.Alternatively, the second insulation layer 250 may include multiplelayers. The second insulation layer 250 may include silicon oxide orsilicon nitride. The second insulation layer 250 may be an interlayerinsulation layer.

The source electrode 260 s and the drain electrode 260 d may be arrangedabove the second insulation layer 250. Each of the source electrode 260s and the drain electrode 260 d may be electrically connected to thesemiconductor layer 220. The source electrode 260 s and the drainelectrode 260 d may be electrically connected to the semiconductor layer220 via contact holes. The contact holes may be formed in the secondinsulation layer 250 and the first insulation layer 230. The sourceelectrode 260 s and the drain electrode 260 d may each include a singlelayer. Alternatively, the source electrode 260 s and the drain electrode260 d may each include multiple layers. The source electrode 260 s andthe drain electrode 260 d may each include one or more materialsincluding aluminum (Al), platinum (Pt), palladium (Pd), silver (Ag),magnesium (Mg), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir),chrome (Cr), lithium (Li), calcium (Ca), molybdenum (Mo), titanium (Ti),tungsten (W), or copper (Cu); however, exemplary embodiments of thepresent invention are not limited thereto. The one or more materials maybe selected according to conductivity.

A protective layer may cover the thin film transistor TFT. Theprotective layer may be configured to protect the thin film transistorTFT. The protective layer may include an inorganic material. Forexample, the protective layer may include silicon oxide, siliconnitride, or silicon oxynitride.

A third insulation layer 270 may be arranged over the flexible substrate100. The third insulation layer 270 may be a planarization layer or aprotective layer. When an organic light-emitting device 290 is arrangedabove the thin film transistor TFT, the third insulation layer 270 mayplanarize an upper surface of the thin film transistor TFT. The thirdinsulation layer 270 may also protect the thin film transistor TFT andvarious devices. The third insulation layer 270 may include, forexample, an acrylic organic material or benzocyclobutene (BCB); however,exemplary embodiments of the present invention are not limited thereto.

As illustrated in FIG. 2, the buffer layer 210, the first insulationlayer 230, the second insulation layer 250, and the third insulationlayer 270 may be formed on the entire surface of the flexible substrate100.

A fourth insulation layer 280 may be arranged above the thin filmtransistor TFT. The fourth insulation layer 280 may be a pixel-defininglayer. The fourth insulation layer 280 may be arranged over the thirdinsulation layer 270. The fourth insulation layer 280 may include anopening. The opening may define a pixel area. The fourth insulationlayer 280 may expose a portion of the pixel electrode 292. The fourthinsulation layer 280 may also cover portions of the pixel electrode 292.For example, the fourth insulation layer 280 may expose a center portionof the pixel electrode 292. The fourth insulation layer 280 may coveredge portions of the pixel electrode 292.

The fourth insulation layer 280 may include, for example, an organicinsulation layer. The organic insulation layer may include an acrylicpolymer such as poly(methyl methacrylate) (PMMA), polystyrene (PS), apolymer derivative containing a phenol group, an imide-based polymer, anaryl ether-based polymer, an amide-based polymer, a fluorine-basedpolymer, a p-xylene-based polymer, a vinyl alcohol-based polymer, or anycombination thereof.

The organic light-emitting device 290 may be arranged over the fourthinsulation layer 280. The organic light-emitting device 290 may includea pixel electrode 292, an intermediate layer 294, and an oppositeelectrode 296. The intermediate layer 294 may include an emission layer(EML).

The pixel electrode 292 may be a semi-transparent electrode, atransparent electrode, or a reflective electrode. When the pixelelectrode 292 is a semi-transparent electrode or a transparentelectrode, the pixel electrode 292 may include, for example, indium tinoxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium oxide(In₂O₃), indium gallium oxide (IGO), or aluminum zinc oxide (AZO). Whenthe pixel electrode 292 is a reflective electrode, the pixel electrode292 may include a reflective layer. The reflective layer may include Ag,Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, or a compound thereof. The pixelelectrode 292 may also include a layer. The layer may include ITO, IZO,ZnO, In₂O₃, IGO, or AZO. However, exemplary embodiments of the presentinvention are not limited thereto. The pixel electrode 292 may includevarious materials. A structure of the pixel electrode 292 may bevariously modified. For example, the pixel electrode 292 may include asingle layer. Alternatively, the pixel electrode 292 may includemultiple layers.

The intermediate layer 294 may be arranged in each pixel area defined bythe fourth insulation layer 280. The intermediate layer 294 may includethe EML. The EML may emit light according to an electrical signal. Inaddition to the EML, the intermediate layer 294 may further include ahole injection layer (HIL), a hole transport layer (HTL), an electrontransport layer, (ETL) and an electron injection layer (EIL). The HTLmay be disposed between the EML and the pixel electrode 292. The EIL maybe disposed between the EML and the opposite electrode 296. The layersmay be stacked in a single or complex structure. However, theintermediate layer 294 is not limited thereto and may have variousstructures.

The opposite electrode 296 covering the intermediate layer 294 includingthe EML and facing the pixel electrode 292 may be arranged over theentire surface of the flexible substrate 100. The opposite electrode 296may be a semi-transparent electrode, a transparent electrode, or areflective electrode.

When the opposite electrode 296 is a semi-transparent electrode or atransparent electrode, the opposite electrode 296 may include a layer.The layer may include metal. The metal may have a relatively low workfunction. For example, the metal may include Li, Ca, lithiumfluoride/calcium (LiF/Ca), lithium fluoride/aluminum (LiF/Al), Al, Ag,Mg, or any combination thereof. The opposite electrode 296 may alsoinclude a semi-transparent conductive layer or a transparent conductivelayer. The semi-transparent conductive layer and the transparentconductive layer may include ITO, IZO, ZnO, or In₂O₃; however, exemplaryembodiments of the present invention are not limited thereto. When theopposite electrode 296 is a reflective electrode, the opposite electrode296 may include a layer. The layer may include Li, Ca, LiF/Ca, LiF/Al,Al, Ag, Mg, or any combination thereof. However, a structure and amaterial of the opposite electrode 296 are not limited thereto.

Referring to FIGS. 2 and 3, the first insulation layer 230 correspondingto a gate insulation layer may be disposed on the entire surface of theflexible substrate 100. At least a portion of the first insulation layer230 arranged over the bending area BA of the flexible substrate 100 mayhave the first unevenness 230 a. The first unevenness 230 a may have astepped shape. The stepped shape may include at least two or more steps.Each step may have a height h1. As illustrated in FIGS. 2 and 3, thefirst unevenness 230 a may have a “V” shape. The first unevenness 230 amay have a stepped shape, which may be sunk toward the center.

A thickness t1 of a portion of the first unevenness 230 a included inthe first insulation layer 230 may be relatively smaller than athickness t2 of a portion of the first insulation layer 230 excludingthe first unevenness 230 a. Thus, the thickness t1 of a portion of thefirst insulation layer 230 in which the first unevenness 230 a is formedmay be relatively smaller than the thickness t2 of a portion of thefirst insulation layer 230 in which the first unevenness 230 a isomitted.

The first unevenness 230 a may include three steps. Each step may havethe height h1 as illustrated in FIG. 3. However, exemplary embodimentsof the present invention are not limited thereto. The first unevenness230 a may include at least one step. The at least one step may have theheight h1. The first unevenness 230 a may be modified according to athickness of the first insulation layer 230 and the height h1.

The first unevenness 230 a may have a width W. For example, the width Wof the first unevenness 230 a may be less than about 1 mm. Asillustrated in FIG. 2, the first unevenness 230 a may be arrangedbetween pixels. Thus the width W of the first unevenness 230 a may berelatively smaller than spaces between adjacent pixels.

The second insulation layer 250 corresponding to an interlayerinsulation layer may be arranged over the first insulation layer 230.The second insulation layer 250 may have the second unevenness 250 a.The second unevenness 250 a may be disposed on the first unevenness 230a. Similar to the first unevenness 230 a, the second unevenness 250 amay be disposed over the bending area BA of the flexible substrate 100.

The second unevenness 250 a may include at least two or more steps. Eachstep may have a height h2. Similar to the first unevenness 230 a, thesecond unevenness 250 a may have a “V” shape. The second unevenness 250a may have a stepped shape, which may be sunk toward the center.

The second unevenness 250 a may include three steps. Each step may havethe height h2. However, exemplary embodiments of the present inventionare not limited thereto. The second unevenness 250 a may include atleast one step. The at least one step may have the height h2. The secondunevenness 250 a may be modified according to a thickness of the secondinsulation layer 250 and the height h2. The first unevenness 230 a andthe second unevenness 250 a may each be formed by using various methodsknown in the art and are not limited to a specific method. For example,the first unevenness 230 a and the second unevenness 250 a may be formedby etching using a photo resist, patterning using a halftone mask, orultrafine printing using screen printing or inkjet printing.

The third insulation layer 270 and the fourth insulation layer 280arranged over the second insulation layer 250 may also be formed in ashape similar to upper surfaces of the first unevenness 230 a of thefirst insulation layer 230 and the second unevenness 250 a of the secondinsulation layer 250. Accordingly, the opposite electrode 296 disposedon the entire surface of an upper surface of the fourth insulation layer280 may also be formed in a shape similar to the upper surface of thefourth insulation layer 280. The formation of the third insulation layer270 and the fourth insulation layer 280 similar to shapes of uppersurfaces of the first insulation layer 230 and second insulation layer250 may provide unevennesses of the third insulation layer 270 and thefourth insulation layer 280 through a separate patterning process. Whenthe third insulation layer 270 and the fourth insulation layer 280 areformed on the entire surface of the flexible substrate 100, the thirdinsulation layer 270 and the fourth insulation layer 280 may have curvesalong a shape of an upper surface of the second unevenness 250 apositioned on lower surfaces of the third insulation layer 270 and thefourth insulation layer 280.

Referring to FIG. 2, the display unit 200 arranged over the flexiblesubstrate 100 may include the plurality of pixels. The first unevenness230 a may be arranged between the plurality of pixels. The plurality ofpixels may be sub-pixels. The plurality of pixels may be pixels formedby collecting sub-pixels.

Referring to FIG. 1, the flexible substrate 100 may have a bending axisA-A. The bending axis A-A may extend in one direction in the bendingarea BA. Thus, the first unevenness 230 a and the second unevenness 250a may extend in a direction substantially parallel to the bending axisA-A. The first unevenness 230 a and the second unevenness 250 a mayextend substantially parallel to the bending axis A-A. Thus, surfaceareas of the first insulation layer 230 and the second insulation layer250 of the flexible display apparatus 1 may relatively increase in thebending area BA. Accordingly, cracks or separation of the firstinsulation layer 230 and the second insulation layer 250 may be reducedor prevented.

The first insulation layer 230 and the second insulation layer 250 mayeach be inorganic insulation layers. Portions of the inorganicinsulation layers positioned over the bending area BA may include thefirst unevenness 230 a and the second unevenness 250 a. Since the firstinsulation layer 230 and the second insulation layer 250 may each beinorganic insulation layers, stress may concentrate and cracks may occurin the bending area BA.

The flexible display apparatus 1 may include the first unevenness 230 aand the second unevenness 250 a disposed in the first insulation layer230 and the second insulation layer 250, respectively. The firstinsulation layer 230 and the second insulation layer 250 may each beinorganic insulation layers. The first insulation layer 230 and thesecond insulation layer 250 may be arranged over the bending area BA.When the flexible display apparatus 1 is bent in the bending area BA,the first unevenness 230 a and the second unevenness 250 a may increasethe surface areas of the first insulation layer 230 and the secondinsulation layer 250. Thus, a stress applied to the first insulationlayer 230 and the second insulation layer 250 may be reduced. Therefore,cracks or separation of the first insulation layer 230 and the secondinsulation layer 250 may be prevented.

FIG. 4 is a schematic cross-sectional view illustrating a bending areaBA of a flexible display apparatus according to an exemplary embodimentof the present invention. FIG. 5 is an enlarged cross-sectional viewillustrating a portion V of FIG. 4 according to an exemplary embodimentof the present invention.

Referring to FIGS. 4 and 5, a flexible display apparatus 2 may includethe flexible substrate 100, the first insulation layer 230, and thesecond insulation layer 250. The first insulation layer 230 may bearranged over the flexible substrate 100. The first insulation layer 230may include the first unevenness 230 a. The second insulation layer 250may be arranged over the flexible substrate 100. The second insulationlayer 250 may include the second unevenness 250 a.

The flexible display apparatus 2 may differ from the flexible displayapparatus 1 of FIG. 1 in shapes of the third insulation layer 270 andthe fourth insulation layer 280 arranged over the first insulation layer230 and the second insulation layer 250, respectively. In the flexibledisplay apparatus 2 of FIG. 4, the third insulation layer 270 may fillgrooves forming the first unevenness 230 a and the second unevenness 250a of the first insulation layer 230 and the second insulation layer 250,respectively. Thus an upper surface of the flexible display apparatus 2may be substantially planarized. The flexible display apparatus 2 ofFIG. 4 may be substantially the same as the flexible display apparatus 1of FIG. 1, and therefore redundant descriptions may be omitted.

According to an exemplary embodiment of the present invention, the firstinsulation layer 230 corresponding to a gate insulation layer may bedisposed on the entire surface of the flexible substrate 100. At least aportion of the first insulation layer 230 arranged over the bending areaBA of the flexible substrate 100 may include the first unevenness 230 a.The first unevenness 230 a may include at least two or more steps. Eachstep may have a height h1. As illustrated in FIG. 5, the firstunevenness 230 a may have a general “V” shape. The first unevenness 230a may have a stepped shape, which may be sunk toward the center.

The first unevenness 230 a may include three steps. Each step may havethe height h1. However, exemplary embodiments of the present inventionare not limited thereto. The first unevenness 230 a may include at leastone step. The at least one step may have the height h1. The firstunevenness 230 a may be modified according to a thickness of the firstinsulation layer 230 and the height h1.

The first unevenness 230 a may have the certain width W. For example,the width W of the first unevenness 230 a may be less than about 1 mm.As illustrated in FIG. 4, the first unevenness 230 a may be arrangedbetween pixels. Thus the width W of the first unevenness 230 a may berelatively smaller than spaces between adjacent pixels.

The second insulation layer 250 corresponding to an interlayerinsulation layer may be arranged over the first insulation layer 230.The second insulation layer 250 may have the second unevenness 250 a.The second unevenness 250 a may be disposed on the first unevenness 230a of the first insulation layer 230. Similar to the first unevenness 230a, the second unevenness 250 a may be arranged over the bending area BAof the flexible substrate 100.

The second unevenness 250 a may include at least two or more steps. Eachstep may have a height h2. Similar to the first unevenness 230 a, thesecond unevenness 250 a may have a “V” shape. The second unevenness 250a may have a stepped shape, which may be sunk toward the center.

The second unevenness 250 a may include three steps. Each step may havethe height h2. However, exemplary embodiments of the present inventionare not limited thereto. The second unevenness 250 a may include atleast one step. The at least one step may have the height h2. The secondunevenness 250 a may be modified according to a thickness of the secondinsulation layer 250 and the height h2. The first unevenness 230 a andthe second unevenness 250 a may each be formed by using various methodsknown in the art and are not limited to a specific method. For example,the first unevenness 230 a and the second unevenness 250 a may be formedby etching using a photo resist, patterning using a halftone mask, orultrafine printing using screen printing or inkjet printing.

The display unit 200 arranged over the flexible substrate 100 mayinclude the plurality of pixels. The first unevenness 230 a may bearranged between the plurality of pixels. The plurality of pixels may besub-pixels. The plurality of pixels may be pixels formed by collectingsub-pixels.

In the flexible display apparatus 2, the flexible substrate 100 may havethe bending axis A-A as illustrated in FIG. 1. The bending axis A-A mayextend in one direction in the bending area BA. Thus, the firstunevenness 230 a and the second unevenness 250 a may extend in adirection substantially parallel to the bending axis A-A. The firstunevenness 230 a and the second unevenness 250 a may extendsubstantially parallel to the bending axis A-A. Thus, surface areas ofthe first insulation layer 230 and the second insulation layer 250 ofthe flexible display apparatus 2 may relatively increase in the bendingarea BA. Accordingly, cracks or separation of the first insulation layer230 and the second insulation layer 250 may be reduced or prevented.

The first insulation layer 230 and the second insulation layer 250 mayeach be inorganic insulation layers. Portions of the inorganicinsulation layers positioned over the bending area BA may include thefirst unevenness 230 a and the second unevenness 250 a. Since the firstinsulation layer 230 and the second insulation layer 250 may each beinorganic insulation layers, stress may concentrate and cracks may occurin the bending area BA.

The flexible display apparatus 2 may include the first unevenness 230 aand the second unevenness 250 a disposed in the first insulation layer230 and the second insulation layer 250, respectively. The firstinsulation layer 230 and the second insulation layer 230 may each beinorganic insulation layers. The first insulation layer 230 and thesecond insulation layer 250 may be arranged over the bending area BA.When the flexible display apparatus 2 is bent in the bending area BA,the first unevenness 230 a and the second unevenness 250 a may increasethe surface areas of the first insulation layer 230 and the secondinsulation layer 250. Thus, a stress applied to the first insulationlayer 230 and the second insulation layer 250 may be reduced. Therefore,cracks or separation of the first insulation layer 230 and the secondinsulation layer 250 may be prevented.

Although a flexible display apparatus according to exemplary embodimentsof the present invention has been described above, exemplary embodimentsof the present invention are not limited thereto. For example, a methodof manufacturing such a flexible display apparatus may also be withinthe scope of the disclosure.

It should be understood that exemplary embodiments of the presentinvention described herein should be considered in a descriptive senseonly and not for purposes of limitation. Descriptions of features oraspects within each exemplary embodiment of the present invention shouldtypically be considered as available for other similar features oraspects in other exemplary embodiments of the present invention.

While one or more exemplary embodiments of the present invention havebeen described with reference to the figures, it will be understood bythose of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. A display apparatus, comprising: a substrateincluding a bending area; and a first insulation layer disposed on thebending area of the substrate, the first insulation layer comprising afirst portion, a second portion, a third portion, and a fourth portionthat are continuously connected to one another, wherein, in an unbentstate of the display apparatus, inclinations of two adjacent portions ofthe first to fourth portions have different angles from each other,relative to the substrate.
 2. The display apparatus of claim 1, whereinthe first portion, the second portion, the third portion, and the fourthportion that are continuously connected to one another form to a steppedshape.
 3. The display apparatus of claim 1, wherein the first insulationlayer comprises an inorganic insulating material.
 4. The displayapparatus of claim 1, wherein the first insulation layer has multiplelayers.
 5. The display apparatus of claim 1, further comprising: a thinfilm transistor and a display element both disposed on the substrate,wherein the thin film transistor includes a semiconductor layer, a gateelectrode having at least a portion overlapping the semiconductor layer,and an electrode layer electrically connected to the semiconductorlayer, and wherein the first insulation layer is arranged between thegate electrode and the electrode layer.
 6. The display apparatus ofclaim 5, further comprising: a second insulation layer disposed on thebending area of the substrate, the second insulation layer comprising afifth portion, a sixth portion, a seventh portion, and an eighth portionthat are continuously connected to one another, wherein, in an unbentstate of the display apparatus, inclinations of two adjacent portions ofthe fifth to eighth portions have different angles from each other,relative to the substrate.
 7. The display apparatus of claim 6, whereinthe second insulation layer is arranged between the semiconductor layerand the gate electrode.
 8. The display apparatus of claim 1, wherein, inan unbent state of the display apparatus, the first portion and thethird portion with the second portion interposed therebetween aresubstantially parallel to the substrate.
 9. The display apparatus ofclaim 8, wherein a top surface of the first portion and a top surface ofthe third portion have different heights with respect to the substrate,and the second portion connects a step difference between the firstportion and the third portion.
 10. The display apparatus of claim 1,further comprising a conductive layer directly disposed on the firstinsulating layer.
 11. The display apparatus of claim 1, wherein thebending region is bent about a bending axis along a first direction andthe third portion extends along the first direction.
 12. The displayapparatus of claim 1, the first to fourth portions have differentinclinations of all two adjacent portions.